Can Pulp Fibroblasts Kill Cariogenic Bacteria? Role of Complement Activation.

Complement system activation has been shown to be involved in inflammation and regeneration processes that can be observed within the dental pulp after moderate carious decay. Studies simulating carious injuries in vitro have shown that when human pulp fibroblasts are stimulated by lipoteichoic acid (LTA), they synthetize all complement components. Complement activation leads to the formation of the membrane attack complex (MAC), which is known for its bacterial lytic effect. This work was designed to find out whether human pulp fibroblasts can kill Streptococcus mutans and Streptococcus sanguinis via complement activation. First, histological staining of carious tooth sections showed that the presence of S. mutans correlated with an intense MAC staining. Next, to simulate bacterial infection in vitro, human pulp fibroblasts were incubated in serum-free medium with LTA. Quantification by an enzymatic assay showed a significant increase of MAC formation on bacteria grown in this LTA-conditioned medium. To determine whether the MAC produced by pulp fibroblasts was functional, bacteria sensitivity to LTA-conditioned medium was evaluated using agar well diffusion assay and succinyl dehydrogenase (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide [MTT]) assay. Both assays showed that S. mutans and S. sanguinis were sensitive to LTA-conditioned medium. Finally, to evaluate whether MAC formation on cariogenic bacteria, by pulp fibroblasts, can be directly induced by the presence of these bacteria, a specific coculture model of human pulp fibroblasts and bacteria was developed. Immunofluorescence revealed an intense MAC labeling on bacteria after direct contact with pulp fibroblasts. The observed MAC formation and its lethal effects were significantly reduced when CD59, an inhibitor of MAC formation, was added. Our findings demonstrate that the MAC produced by LTA-stimulated pulp fibroblasts is functional and can kill S. mutans and S. sanguinis. Taken together, these data clearly highlight the function of pulp fibroblasts in destroying cariogenic bacteria.

Effect of dual cure composite as dentin substitute on the marginal integrity of Class II open-sandwich restorations.

This study compared the marginal adaptation of Class II open-sandwich restorations with an RMGIC versus a dual-cure composite as dentin substitute. Class II cavities were prepared on 50 extracted human third molars. The teeth were randomly assigned to two groups of 25 teeth to compare one dual cure composite (Multicore Flow) with one resin-modified glass-ionomer cement (Fuji II LC) in open-sandwich restorations covered with a light cure composite. The teeth were thermomechanically cycled (2000 cycles, 5 degrees C to 55 degrees C; 100,000 cycles, 50 N/cm2). The specimens were then sealed with a 1 mm window around the cervical margin interface. Samples were immersed in a 50% w/v ammoniacal silver nitrate solution for two hours and exposed to a photodeveloping solution for six hours. The specimens were sectioned longitudinally and silver penetration was directly measured using a light microscope. The results were expressed as a score ranging from 0 to 3. The data were analyzed with a non-parametric Kruskall and Wallis test. The degree of leakage significantly increased with Multicore Flow (median = 2) compared to Fuji II LC (median = 1). The resin-modified glassionomer cements remain the best intermediate materials when open-sandwich restorations are indicated. A comparison of the degradation of these materials over time remains a topic to be investigated by future studies.

Effect of dual cure composite as dentin substitute on marginal integrity of class II open-sandwich restorations.

The current study compared the marginal adaptation of Class II open-sandwich restorations with a RMGIC versus a dual-cure composite as dentin substitute. Class II cavities were prepared on 50 extracted human third molars. The teeth were randomly assigned to two groups of 25 teeth to compare one dual cure composite (MultiCore Flow) with one resin-modified glass-ionomer cement (Fuji II LC) in open-sandwich restorations recovered with a light cure composite. The teeth were thermomechanocycled (2000 cycles, 5 degrees C to 55 degrees C; 100,000 cycles, 50 N/cm2). The specimens were then sealed with a 1 mm window around the cervical margin interface. Samples were immersed in a 50% w/v ammoniacal silver nitrate solution for two hours and exposed to a photo-developing solution for six hours. The specimens were sectioned longitudinally and silver penetration was directly measured using a light microscope. The results were expressed as a score from 0 to 3. The data were analyzed with a non-parametric Kruskal and Wallis test. The degree of leakage significantly increased with MultiCore Flow (median 2) compared to Fuji II LC (median 1). Resin-modified glassionomer cements remain the best intermediate material when open-sandwich restorations are indicated. A comparison of the degradation of these materials over time remains a topic to be investigated by future studies.

Clinical evaluation of the marginal fit of cast crowns--validation of the silicone replica method.

Replication of the space between a tooth and its cast crown, using a light-body silicone supported by a heavy-body silicone, is a recognized technique to evaluate the quality of a restoration. This study validates a similar method that is of great clinical and experimental interest. Whatever the type of silicone used, comparison is possible between different technical procedures of crown elaboration (type of impression, type of material, method of spacing, etc.). If an appropriate silicone is used, the cement space may be reproduced and its thickness measured, whatever the localization (cervical, axial, occlusal).

Human biological reactions at the interface between bone tissue and polymethylmethacrylate cement.

This study investigated cytotoxicity of cement fragments harvested from two prosthesis revisions by the MTT test using L929 fibroblasts and human osteoblasts. The results did not show any toxicity of the extracts prepared after 48 and 78 months implantation. We consider that no MMA monomer has been released from the cement fragments. Histological studies on undecalcified samples harvested around revising prosthesis from 11 patients were used to evaluate tissue reactions at the bone-cement interface after 2-168 months implantation. Cement and prosthesis particles (5-35 microm) either dispersed or forming a layer were observed. A fibrous tissue layer, osteolysis, and osteonecrosis areas were observed at the interface. Besides, fibroblasts, macrophages, and multinucleated giant cells were also observed. New bone formation with osteoid, osteoblasts, and endochondral ossification with fibrocartilaginous tissue has been observed. The tissue reactions seemed to decrease with time. However, osseous trabeculae fractures were observed in the samples after 19 months. Although we consider that monomer toxicity, exothermic reaction, and particles formation may cause short-term prosthesis loosening; the trabeculae fractures may be due to prosthesis and bone cement micromovements. This fractures and particles formation may cause long-term prosthesis loosening.

In vivo diagnostic assessment of dentinal caries by junior and senior students using red acid dye.

The aim of this study was firstly to determine and compare the ability of inexperienced junior dental students (Fourth-year) and senior students (Fifth-year) versus a dental school instructor to identify demineralized dentine with the aid of a caries-disclosing solution and secondly to evaluate an eventual improvement of the caries diagnosis accuracy of junior (Fourth-year) and senior (Fifth-year) dental students. Three successive stages were used to check the ability of the dental students to diagnose and excavate the de-mineralized dentine. This study pointed out that 96% of junior dental students versus a teacher failed to remove all of the demineralized dentine without the use of a caries detector at the first stage and 79% at the second stage in the same condition. 100% of senior students versus a teacher, also failed to diagnose dental caries without a caries detector, but only at the first stage. However, at the second stage, unlike the junior students, all of the senior students were able to remove all of the demineralized dentine. Without the use of a caries detector dye, the risks of the dental students leaving demineralized dentine are high. This technique may be particularly helpful for the fourth-year students who are performing their first restorative treatment.

In vitro assessment of polymerization procedures in Class II restorations: sealing, FTIR, and microhardness evaluations.

PURPOSE: This study was undertaken to evaluate several polymerization and filling procedures (incremental, bulk, light-tip, soft-cured, plasma devices) in Class II restorations through (1) a sealing evaluation of restorations filled with Tetric Ceram (TC) and Bisfil 2B (B2B, self-cured composite used as a control), (2) a FTIR analysis measuring the variations of the degree of conversion in terms of area unit ratio of the relevant resin composites and (3) a microhardness test to corroborate the FTIR analysis. MATERIALS AND METHODS: The length of the tracer penetration was measured from the gingival margin up to the cavity wall with an episcope on sectioned teeth. A ceramic mould, simulating a Class II, was filled according to the different groups and the samples were analyzed with a Bruker IFS 55 spectrometer on ultrathin sections (3 mu). The results were analyzed in terms of area unit ratio and total exposed energy. Under the same conditions, a microhardness test was run with a Frank Weihem machine. RESULTS: The results of the sealing evaluation for light-tip, incremental and self-cured techniques did not differ. The plasma procedure failed in this evaluation as the bottom increment was not polymerized. The smallest area unit ratio (the best degree of conversion) was observed in 2 groups: one, the combination of the light-tip and soft process, and two, the self-cured resin composite (B2B). The distance at which the plasma procedure failed to cure the resin composite was between 3.5 and 4.5 mm. The microhardness test confirmed the FTIR analysis except for the group G2 (TC + light-tip). As also shown by FTIR analysis, no difference between the two relevant levels was observed with the hardness test. CONCLUSION: The dentin marginal sealing efficiency of Tetric Ceram restorations was increased with the light-tip technique, but was not better than the self-cured resin composite (B2B). For Tetric Ceram, the combination of the light-tip and soft process leads to a higher degree of conversion than the other groups. There is no linear relationship between the degree of conversion, the microhardness and the total exposed energy. The combination of the soft polymerization and the light-tip device might be an alternative restorative technique to the current incremental technique.

Reliability of in vitro microleakage tests: a literature review.

PURPOSE: The literature contains conflicting data about in vitro microleakage evaluations and their usefulness and reliability. No standardization has yet been established. Here we consider features of published studies that might affect the results of the in vitro microleakage tests. MATERIALS AND METHODS: We reviewed 144 in vitro microleakage studies, published in 14 international reviews between 1992 and 1998, which comprised 917 sets or groups of experiments. The published studies were entered in a database and compared using selected literature criteria: sample, cavities, restoration procedures, thermocycling and mechanical cycling, evaluation method. RESULTS: The methods employed vary widely. The most frequent methodological choices (%) were (1) specimen storage after extraction: duration (unspecified, 59.2), medium (distilled or deionized water, 33.8), temperature (unspecified, 52.2), additives (none, 47.0); (2) aging method (79.1): duration before aging (< 24 h, 35.9); medium and temperature of storage before aging (distilled or deionized water, 26.8; 37 degrees C, 54.3); (3) medium of cycling (tap water, 50.5), number of cycles ([250-500], 34.6), number of baths (2, 84.0), bath temperature (5 degrees C to 55 degrees C, 60.6), immersion dwell time (30 s, 44.3); (4) tracer: type (basic fuchsin, 40.7), time of immersion (after thermocycling and/or mechanical cycles, 64.1), immersion duration (basic fuchsin: 24 h, 59.5); assessment of dye penetration of sections (91.7): direction (perpendicular, 88.5), number (1, 47.1). CONCLUSION: The great variability in the methods used in these 144 studies prevented meta-analysis and comparison of the results, thus reducing the value of these methods.

Factors influencing pulpal response to cavity restorations.

OBJECTIVES: The purposes of this retrospective work were: (1) to determine the relative importance of bacteria on cavity walls, remaining dentin thickness and post-operative time on pulpal inflammation after cavity restoration; (2) to compare the respective influences of bacterial microleakage and the restorative material itself on pulp reaction severity. METHODS: 317 class V cavities, in human bicuspids scheduled for extraction for orthodontic reasons were used for this study. Nine different materials were included. The severity of the pulpal reaction was ranked on hematoxylin/eosin stained sections according to FDI standards. The further parameters recorded were: (1) the presence or absence of bacteria on the cavity walls was noted on Brown and Brenn stained sections; (2) the remaining dentin thickness was measured and the teeth classified into three groups (< 500, 500-1000, > 1000 microns); and (3) the post-operative delay before extraction was recorded and classified as short time (< 5 weeks) or long time (> 5 weeks). Three two-way analyses of variance (ANOVA) followed by Kruskall and Wallis tests evaluated the influence of the three parameters on pulpal reaction severity. The third ANOVA also compared pulpal reactions under the different materials when the teeth were pooled, on bacteria free teeth and on bacteria contaminated teeth. RESULTS: The first ANOVA ranked by decreasing order of importance: the presence of bacteria (p < 0.0001), the remaining dentin thickness (p = 0.02) and the post-operative delay (p = 0.04). The second ANOVA showed no difference among the restorative materials when bacteria were present on the cavity walls. SIGNIFICANCE: The presence of bacteria on the cavity walls is the main factor influencing pulpal reaction under restorative materials, but does not account for 100% of the cases.

Histological and biomechanical studies of two bone colonizable cements in rabbits.

We have developed two colonizable bone cements: the first is a partially resorbable bisphenol-alpha-glycidyl methacrylate (Bis-GMA)-based cement (PRC) and the second is a calcium phosphate cement (CPC). PRC is composed of aluminous silanized ceramic and particles of a bioresorbable polymer embedded in a matrix of Bis-GMA. CPC consisted of tricalcium phosphate, monocalcium phosphate monohydrate, dicalcium phosphate dihydrate, and xanthane. Both cements were implanted into cavities drilled in rabbit femoral and tibial condyles. After 2, 4, 12, and 24 weeks of implantation, histological observations and biomechanical tests were performed. With CPC, a progressive osteointegration with a concomitant biodegradation in the presence of macrophages were observed. The mechanical study revealed a decrease of the compressive strength until the 4th week, followed by a slight increase. There was a general decrease in the elastic modulus with time. Moreover, by week 4, the histological study showed that the new bone was in direct contact with CPC margins. No inflammation was observed during the observation period. With PRC, the osteointegration as well as the biodegradation were slight, but its compressive strength was higher than that of cancellous bone and CPC (p < 0.05) at all observation periods. Its elastic modulus was greater than that of cancellous bone and CPC until the 4th week, then fell under the values of the cancellous bone.

Low-energy He/Ne laser in the prevention of radiation-induced mucositis. A multicenter phase III randomized study in patients with head and neck cancer.

Use of the low-energy helium-neon laser (LEL) appears to be a simple atraumatic technique for the prevention and treatment of mucositis of various origins. Preliminary findings, and significant results obtained for chemotherapy-induced mucositis in a previous phase III study, prompted a randomized multicenter double-blind trial to evaluate LEL in the prevention of acute radiation-induced stomatitis. Irradiation by LEL corresponds to local application of a high-photon-density monochromatic light source. Activation of epithelial healing for LEL-treated surfaces, the most commonly recognized effect, has been confirmed by numerous in vitro studies. The mechanism of action at a molecular and enzymatic level is presently being studied. From September 1994 to March 1998, 30 patients were randomized. Technical specification: 60 mW (25 mW at Reims, 1 patient), He-Ne, wavelength 632.8 nm. The trial was open to patients with carcinoma of the oropharynx, hypopharynx and oral cavity, treated by radiotherapy alone (65 Gy at a rate of 2 Gy/fraction, 5 fractions per week) without prior surgery or concomitant chemotherapy. The malignant tumor had to be located outside the tested laser application areas (9 points): posterior third of the internal surfaces of the cheeks, soft palate and anterior tonsillar pillars. Patients were randomized to LEL or placebo light treatment, starting on the first day of radiotherapy and before each session. The treatment time (t) for each application point was given by the equation : t(s)= energy (J/cm2) x surface (cm2)/Power (W). Objective assessment of the degree of mucositis was recorded weekly by a physician blinded to the type of treatment, using the WHO scale for grading of mucositis and a segmented visual analogue scale for pain evaluation. Protocol feasibility and compliance were excellent. Grade 3 mucositis occured with a frequency of 35.2% without LEL and of 7.6% with LEL (P<0.01). The frequency of "severe pain" (grade 3) was 23.8% without LEL, falling to 1.9% with LEL (P<0.05). Pain relief was significantly reduced throughout the treatment period (weeks 2-7). LEL therapy is capable of reducing the severity and duration of oral mucositis associated with radiation therapy. In addition, there is a tremendous potential for using LEL in combined treatment protocols utilizing concomitant chemotherapy and radiotherapy.

Shock absorbability of various restorative materials used on implants.

The purpose of this study was to compare, using an in vitro model, the stress absorbing ability of a microfilled composite resin and of a new low fusion ceramic (Duceram LFC) to that of gold alloy and conventional ceramic, when used as restorative materials in implant-supported prosthesis. Test crowns made of the tested materials were rigidly connected to a Brånemark implant clone. The maximum amplitude of the force transmitted to the bone-implant interface, and the time to reach this amplitude were measured after applying a 100 N impact load on the occlusal surface. The gold alloy restorations transmitted the highest impact force in the shortest delay at the bone-implant interface. Microfilled composite resin Dentacolor, and low fusion ceramic Duceram LFC did not reduce the amplitude of the impact-force when compared to conventional ceramic. Nevertheless, the time to reach the maximum amplitude of this force was longer when using composite resin than when using ceramic, while Duceram LFC had no influence on this criteria.

[Interbody arthrodesis using a plasmapore titanium block. Mechanical and histological experimental study in sheep]. / Arthrodèse intersomatique par l'intermédiaire d'un bloc titane Plasmapore. Etude expérimentale mécanique et histologique chez la brebis.

UNLABELLED: A Plasmapore-coated titanium alloy block was implanted in ewes for the purpose of providing interbody fusion. Four blocks were implanted in each ewe: one uncoated block (without Plasmapore) serving as a reference specimen and three blocks coated with Plasmapore. Mechanical testing and histological study were performed on five ewes. OBJECTIVES: Determination of the quality of the mechanical and histological anchorage of the Plasmapore implanted in the interbody space in the same animal living under conditions of physical strain exerted on the spine. METHODS: Four months after surgical implantation of the block, the ewes were sacrificed: the removed spines were frozen for subsequent mechanical analysis and preserved in a solution of 40 degrees alcohol for subsequent histological analysis. X-rays were taken to evaluate the positioning of the implant. The mechanical analysis included extraction tests, measuring the maximum extraction force and evaluating the stiffness of the system, being indicative of the mechanical fixation quality. The histological study included both qualitative and quantitative analysis, together with an evaluation of the osteointegration of the blocks coated with Plasmapore. RESULTS: After 4 months of implantation, a mean extraction force of 990 N was necessary for the blocks coated with Plasmapore, and of 1.338 N for the blocks coated with Plasmapore with additional osteosynthesis, whereas a mean extraction force of 332 N was necessary for the uncoated blocks. Anchorage and resistance against uprooting of the blocks coated with Plasmapore were significantly more efficient. The histological study revealed the presence of bone neoformation adhering to the implant. Quantification of this bone formation covering nearly 45% of the implant perimeter, confirmed both osteointegration of the implant perimeter, confirmed both osteointegration of the implant surfaces being in contact with the vertebral endplates and osteoconduction along the lateral surfaces. CONCLUSION: The titanium Plasmapore block enables interbody fusion due to an osteointegration of the vertebral endplates by Plasmapore coating, which was proved by the results of extraction testing and histological study. It should be taken into account that no additional bone grafts have been used and that the implant had not been forced into the spongiosa.

Comparative clinical study of a bioabsorbable membrane and subepithelial connective tissue graft in the treatment of human gingival recession.

BACKGROUND: Connective tissue grafts and guided tissue regeneration (GTR) are the most current procedures in the treatment of gingival recession, but very few clinical comparative studies have been conducted. METHODS: The purpose of this study was to compare 2 types of treatment of gingival recession in the same patients. Fourteen pairs of Miller Class I defects were selected in 14 patients. In each pair, one recession was randomly assigned for treatment by GTR using a bioabsorbable membrane, and the other treated by subepithelial connective tissue graft (CTG). Height of recession (HR), clinical attachment level (CAL), probing sulcus depth (PSD), height of keratinized tissue (HKT), and distance from the cemento-enamel junction to the mucogingival junction (CEJ-MGJ) were recorded before surgery and 6 months postoperatively. RESULTS: The initial width and height of recession were, respectively, 3.73 mm (SD 0.56) and 3.85 mm (SD 1.15) for the CTG group, and 4.04 mm (SD 0.92) and 4.28 mm (SD 1.20) for the GTR group. The differences were not significant. CAL changes were not different. Both in the CTG group and in the GTR group, mean HR reduction was 2.89 mm (SD 1.18), representing a mean root coverage of 76% and 70.2%, respectively. The difference was not significant. HKT mean gain was significantly greater (P = 0.0001) with CTG (2.03 mm, SD 0.92) than with GTR (0.42 mm, SD 0.91). The GTR technique displaced the mucogingival junction significantly (P = 0.007) more coronally (2.35 mm, SD 1.44) than the CTG technique (0.78 mm, SD 1.23). CONCLUSIONS: Within the limits of this study, no difference could be found between subepithelial connective tissue graft and GTR with a bioabsorbable membrane with regard to root coverage, but the GTR technique did not increase the height of keratinized tissue and displaced the mucogingival junction more coronally at 6 months.

Comparison of two implantation sites for testing intraosseous biocompatibility.

The purpose of this study was to compare two implantation sites--the mandible and the femur of the rabbit--for testing in vivo intraosseous biocompatility. Twenty-two new Zealand rabbits were anesthetized, and the mandibular and femur bones were exposed. A hybrid glass ionomer cement or zinc oxide eugenol cement was loaded into silicone carriers and inserted into the two bones after drilling the two cortical plates. Eleven rabbits were killed 4 wk after implantation, and 11 rabbits were killed after 12 wk. The mandibles and femurs were prepared using standard histological procedures; tissue reactions were graded from none to severe. At 4 wk, no statistically significant difference was found between the two implantation sites. After 12 weeks, bone healing was statistically better in the mandible than in the femur. The mandible seems to be a better implantation site in the case of intraosseous implantation tests. The intraosseous biocompatibility of Vitremer was similar at 4 wk and superior at 12 wk to that of Super-EBA.

Relationship between dentine hydraulic conductance and the cytotoxicity of four dentine bonding resins in vitro.

OBJECTIVES: Dentine modifies pulpward diffusion of monomers leaching from restorative materials. Thus, remaining dentine thickness must be taken into account during in vitro cytotoxicity tests. This in vitro study was designed to determine the influence of dentine permeability on the outcome of a cytotoxicity test. METHODS: Dentine slices were made from 36 human third permanent molar teeth. The 36 dentine slices were divided into two groups according to their hydraulic conductance: high or low hydraulic conductance. The cytotoxicity of four dentine bonding agents of similar cytotoxicity was tested on dentine slices from each group. Four dilutions of the experimental culture medium were tested: undiluted, 1:2, 1:10 and 1:100. An analysis of variance was used to compare the cytotoxicity of the dentine bonding agents tested on high versus low hydraulic conductance. RESULTS: The cytotoxicity of the high hydraulic conductance (Lp) group was higher than that of low Lp group when tested with the undiluted test culture medium (p = 0.001). No difference was obtained with the 1:2, 1:10, 1:100 dilutions. CONCLUSIONS: Under the conditions of the study, the dentine bonding resins were more cytotoxic when applied onto dentine slices of high hydraulic conductance.

Immunocytochemical detection of apoptosis in human odontoblasts.

Pulpal chamber size decreases on ageing due to primary and secondary dentin deposition. This work was designed to find out the consequences of this pulp chamber reduction on odontoblast number and distribution. Twenty-one healthy human premolars were equally divided into three groups from 11-, 12.5- and 14-yr-old adolescents, respectively). The external and the internal perimeters of dentin were recorded on vestibulo-lingual sections, from buccal to lingual cemento-enamel junction using an image analysis system. Nuclei of the odontoblasts were recorded on 12 automatically selected fields. On nine erupted premolars (3 teeth from each 11-, 12.5- and 14-yr-old patients), apoptosis was detected by confocal microscopy using a modification of the original TUNEL method. Apoptotic cells were labeled in central pulp fibroblasts, perivascular endothelial cells, and in odontoblasts. When the pulp volume decreases due to primary dentin production, the decrease of the surface available for odontoblasts is compensated for by a multilayer distribution of cells. Secondary dentin deposition, associated with odontoblasts reorganization in a single layer, results in a hyperbolic decrease of the odontoblasts number. This decrease seems to result from a programmed cell death, which eliminates half of the odontoblasts over a 4-yr period.

Effects of desensitizing agents on human dentin permeability.

PURPOSE: To compare the in vitro effects of three desensitizing agents on hydraulic conductance of human dentin: Protect (n = 10), Gluma Desensitizer (n = 10), MS Coat (n = 10) (Pain-Free in the USA). MATERIALS AND METHODS: Dentin discs were prepared from 40 freshly extracted normal human third molars. The pulpal side of the dentin discs was etched with 37% phosphoric acid for 15 s and then rinsed under tap water. The coronal side was sequentially ground and the dentin discs were sonicated for 30 min. The hydraulic conductance was measured filtering 20% serum in phosphate buffered saline under a pressure of 15 cm H2O. The hydraulic conductance of each dentin specimen was measured before using the desensitizing agent and this value was designated as 100%. Thirty dentin discs were treated, the hydraulic conductance was remeasured and expressed as a percentage of the hydraulic conductance of that specimen before treatment. The teeth were stored for 1 month at 37 degrees C in deionized water and the hydraulic conductance of the 40 dentin discs was recorded again. Ten dentin discs were left untreated to serve as a control. RESULTS: No statistical difference was found between the immediate hydraulic conductance of the three groups after treatment. After 1-month storage, the control group showed a statistically higher hydraulic conductance than the three treated groups. There was no statistical difference between the three dentin desensitizing agents evaluated.

Eugenol diffusion through dentin related to dentin hydraulic conductance.

OBJECTIVES: The purpose of this study was (1) to find an easy way of evaluating the concentration of eugenol in cell culture fluids; (2) to confirm the relationship between the concentration and the cytotoxicity of eugenol in vitro; (3) to evaluate the cytotoxicity of four temporary eugenol-based filling materials: IRM, super EBA, Kalsogen and zinc oxide-eugenol cement; and (4) to establish a relationship between dentin permeability, eugenol diffusion and cytotoxicity. METHODS: (1) The concentration of eugenol was measured with a spectrofluorimeter; (2) the cell viability of L 929 cells cultivated for 24 h with eugenol-containing medium was evaluated by the MTT assay; (3) after measurement of hydraulic conductance, occlusal cavities in human teeth in vitro were filled with the restorative materials. The cytotoxicity was measured with undiluted test medium and with various dilutions in culture medium; (4) after Lp measurement, the eugenol concentration in the media in the pulp chamber that diffused from IRM and 10(3) mol/l eugenol solution was measured. RESULTS: (1) A proportional relationship (p = 0.001 and r = 1) was found between the concentration of eugenol; (2) eugenol started to be cytotoxic at 10(-5) mol/l and killed 95% of the cells at 10(-3) mol/l; (3) zinc oxide-eugenol cement was the most cytotoxic filling material when tested with the 1:100 dilution; (4) a significant relationship was found between Lp and cytotoxicity (p = 0.04) depending on the dilution of the test medium. A significant relationship was found between Lp and eugenol diffusion from a 10(-3) mol/l solution (p = 0.03) but not between Lp and eugenol diffusing from solid IRM (non significant). SIGNIFICANCE: Eugenol diffusion from zinc oxide-eugenol cement appears to depend more on the role of hydrolysis of eugenol from zinc oxide-eugenol cement than on dentin permeability.

Low versus high pressure for in vitro determination of hydraulic conductance of human dentine.

The purpose of this study was to evaluate the effect of applied pressure and measurement time on the in vitro measurement of hydraulic conductance of human dentine. Dentine slices were prepared from 50 third molars. Water was forced through the slices under a constant hydrostatic pressure. Five pressures were tested: 1.3 kPa (n = 10), 13.3 kPa (n = 10), 26.6 kPa (n = 10), 40 kPa (n = 10) and 53.3 kPa (n = 10). The volume that went through the slices was recorded every 10 min for 3 h. The volume, the fluid flow rate and the hydraulic conductance under the five pressures were compared. The volume increased with time and pressure. The fluid flow and hydraulic conductance decreased with time under 13.3, 26.6 and 40 kPa, but remained constant under 1.3 and 53.3 kPa. Used of a low pressure (1.3 kPa) may permit water to pass through dentinal tubules without disturbing intratubular contents. Medium pressures (13.3, 26.6, 40 kPa) seemed to disturb tubule contents progressively, resulting in decreased fluid flow and therefore a decreased hydraulic conductance with time. Under these pressures, the calculated values of hydraulic conductance may be unreliable because they are time-dependent. High pressure (53.3 kPa) seemed to pack the tubule contents against intratubular resistances immediately, resulting in low fluid flows and low hydraulic conductances.